Process of making titanium alloy articles



3,496,036 PROCESS OF MAKING TITANIUM ALLOY ARTICLES Vincent N. Di Giambattista, Trafford, Pa., assignor to Penn Nuclear Corporation, a corporation of Pennsylvania No Drawing. Filed May 25, 1967, Ser. No. 641,155 Int. Cl. C21d 1/74 U.S. Cl. 148126 8 Claims ABSTRACT OF THE DISCLOSURE Making porous highly ductile type titanium alloy articles by the isostatic reconsolidation, vacuum sintering and non-reactive gas quenching of low oxygen content titanium alloy powder.

- The present invention relates generally to' a powder metallurgy process for the production of titanium base alloy articles from low intersticial contaminantcontaining titanium base alloy metal powders. More particularly,

followed by the sintering or machining and then sintering of the green isostatically reconsolidated article which is subsequently annealed and quenched in an inert atmosphere so as to produce relatively ductile, titanium base articles produced by a powder metallurgy process which articles are characterized by a relatively high modulus of elasticity.

Many patents have been granted on titanium base alloys, articles and processes of producing titanium base alloys, powders and the like. Some of the patents are directed to attempts to improve the ductility of the titanium base alloys'and articles while other patents are directed to'titanium base alloys and articles presumably characterized by a greatly improved modulus of elasticity. It -is-well-known that titanium base alloys containing overapproximately 75% titanium are very difficult and costly to machine and fabricate. Despite all alloy articles produced by processes known heretofore are generally characterized by a relativelylo'w ductility and modulus of elasticity." 7

Accordingly, it is the primary object of the present invention to provide a novel process of making titanium base alloy articles by a powder metallurgy technique so as to produce titanium base alloy articles characterized by a relatively high ductility and modulus of elasticity.

Another object of the present invention is to provide a novel powder metallurgy process for the production of isostatically reconsolidated, sintered and annealed microscopically porous titanium base alloy articles characterthe work that'has been done in the field titanium base 3,496,036 Patented Feb. 17, 1970 ice ized by a relatively high ductility and modulus of elasticity.

A further object of the invention is to provide a novel powder metallurgical process for the production of titanium base alloy articles from a low interstitial contaminant containing titanium base alloy powder produced such as by the free impact comminution or vacuum melting of titanium base alloy in an inert atmosphere.

Still another object of the present invention is to provide a novel powder metallurgical process of forming relatively ductile titanium base alloy rivets having a greatly improved highly modulus elasticity which may be readily cold-headed without cracking, fracturing or otherwise deteriorating so as to overcome many of the problems encountered when attempting to cold-head rivets Wrought from solid titanium base alloy.

Still another object of the present invention is to provide a novel powder metallurgical process for the production of thin wall tubing characterized by a microscopic porosity, relatively high ductility and greatly improved modulus of elasticity.

A further object of the invention is to provide a novel powder metallurgical process for the production of a microscopically porous thin wall titanium base alloy tubing suitable for use in hydraulic systems and like wherein the tube is particularly adapted to operate at a given pressure which tubing does not rupture or burst at pressures greatly in excess thereof inasmuch as the microscopically porous tubes are capable of allowing excess pressure to bleed off through the microscopic pores rather than cause bursting of the tube.

Further objects and aspects of the invention will become apparent from the following discussion.

Briefly, the process of the present invention for the production of titanium base alloy articles starts with the free impact comminution of titanium base alloy billets such as of 90% titanium6% aluminum-4% vanadium conforming to AMS 492842, for example, or of 92.5% titanium-5 aluminum-2.5% vanadium and like. The resulting titanium base alloy powder is of a mesh suitable for use in a powder metallurgical process and accordingly would be on the order of approximately 80 to 325 mesh Tyler Standard. The primary interstitial contaminants which normally adversely affect the carrying forth of the process of the present invention comprise. gaseous hydrogen, nitrogen and oxygen. It will therefore be appreciated that 'when reducing the titanium base alloy billet to a suitable powder it is preferable to subject the interior of the apparatus within which the billet is comminuted to a high vacuum so a's to exhaust as much of the gaseous contaminants as possible after which the apparatus is backfilled with an ultra-pure helium to a pressure slightly above the ambient pressure exerted on the apparatus so as to substantially preclude the seepage of such gaseous contaminants into the interior of the comminuting apparatus during powdering of the billet. Merely by way of example a forged cleaned billet comminuated in the manner described hereinabove might initially contain 40 ppm. hydrogen, ppm. nitrogen and 1600 ppm. oxygen prior to comminution and only show an increase of approximately 50 ppm. in the oxygen content without any measurable increasein the hydrogen or nitrogen content thereof subsequent to comminution. Inasmuch as titanium and its alloys have a very high afi'inity for gaseous oxygen, nitrogen and hydrogen With the aforementioned parameters in mind the low interstitial contaminant containing titanium base alloy powder is reconsolidated to form green i.e. unsintered, compacts of suitable configurations. The pressure reconsolidation of thetitanium base alloy powder is preferably accomplished by isostatically reconsolidating the powder by pressing in a double-ram metal powder press utilizing a carbide die, for example, with rather high pressures ranging from approximately 40,000 p.s.i. to 100,000 p.s.i. so as to produce a green compact which may if desired be machined to a specific configuration prior to the carrying forth of the succeeding manipulative steps of the process of the present invention. It will be appreciated that substantial economies are realized by machining the reconsolidated titanium base alloy articles prior to sintering and further heat treatment. The reconsolidation preferably results in a production of an intermediate titanium base alloy powder metallurgical article having a density of approximately 85% to 94% of the theoretical density.

Subsequent to the reconsolidation of the low interstitial contaminant containing titanium base alloy powder to form an article of a desired configuration, followed by machining if required, the article is subjected to a sintering procedure wherein the article is raised to a temperature of approximately 2100 F. to 2200 F. in a vacuum furnace, for example, evacuated to a pressure of x10-? r 4 4 metal powder showing an increase of only 50 ppm. oxygen over that of the billet.

Table I Chemistry of billet: Percent C .02 N .006 H .004 Fe .09 Al 6.6 V 4.3 0 .160

Properties of billet:

Ultimate, k.s.i 146.1 Yield, k.s.i 136.7 Elongation, percent 14.0 R.A., percent 40.1 Hardness: R 36-37.5 Beta transus, F. 1833 Static notch, p.s.i 175,000

1 For 6 hours without rupturing.

I The titanium base alloy metal powder thus produced was pure argon gas to a partial pressure of 24 in./Hg in order mm./Hg, and backfilled with ultra-pure argon to a partial pressure so as to preclude the volatization or vaporization of alloy elements, such as aluminum, tin, etc. The metal powder parts are held at the aforementioned temperature for a period of approximately four hours during which the density of the parts increases to approximately 95% of theoretical. Subsequent to the four hour holding period the furnace temperature is dropped to approximately 1725 F. to 1750 F. and held in this temperature range for approximately one hour to initiate the annealing of the sintered reconsolidated titanium base alloy article. Subsequent, to the aforementioned one hour holding, the furnace temperature is gradually reduced, preferably in approximately one hour, to approximately 1,000 F. to 1,100 F. followed by a quenching to approximately room temperature in a flow of inert gas such as might 'be accomplished by the utilization of cold recirculating ultrapure Argon to produce a final product having properties which, heretofore, were unattainable in titanium base alloy articles containing a minimum of 75% titanium. Furthermore, microscopically porous titanium base alloy articles made by the aforementioned process show increased improvement in machinability in the order of approximately 30-40%, a significant increase in ductility and greatly improved modulus of elasticity.

The following examples are included to more specifically illustrate the practice of the present invention.

EXAMPLE I A 90 titanium--6 aluminum-6 vanadium .forged cleaned billet conforming means to AMS 4928-0 and having the approximate analysis and properties set forth in Table I was converted to a low interstitial contaminant containing metal powder wherein the majority of the particles was'approximately 200 mesh Tyler Standard by subjecting the forged cleaned billet to a comminution procedure comprising reducing the billet to chips which were cleaned and then subjected to free impact comminution in a substantially inert atmo p so as to Produce a to preclude the volatization or vaporization of the alloying aluminum. The vacuum furnace was then heated to a temperature of approximately 2100" F. to 2200 F., in seven minutes and then held at that temperature for a period of approximately four hours. The furnace temperature was then rapidly dropped to approximately 1750 F. and held there for about one hour to initiate annealing of the sintered tensile test bars. The furnace temperature Was then gradually reduced from 1750 F. to approximately 1100 F., which required approximately 50 minutes. The tensile test bars were then quenched from 1100 F. to approximately room temperature in a cold recirculating flow of ultra-pure argon gas. From the data set forth in Table II, it will be appreciated that this process produces a most satisfactory titanium base alloy article exhibiting high tensile strength, good deformation characteristics and a substantially improved modulus'elasticity which shows an increase in improvement in machineability in the order of approximately 30-40% so as to provide a pressure sintered and heat-treated titanium base alloy article having desirable physical properties not heretofore attainable.

0.160 lb./in

' EXAMPLE II Low interstitial contaminant containing titanium base alloy powder produced as set forth in Example I was reconsolidated by cold pressing in a double-acting press at a pressure of 100,000 p.s.i. into the configuration of rivets such as utilized by the aircraft industry for the fabrication of aircraft fuselages and the like. The rivets were then sintered by heating to approximately 2200 F. and holding at such temperature for approximately four hours in a furnace, such as described in Example I, after which the temperature in the furnace was quickly dropped to approximately 1725 F. and held at that temperature for an hour. The rivets were then quenched with cold Argon from a temperature of 1725 F. down to 1000 F. in approximately three minutes and then permitted to gradually cool to room temperature with additional amounts of ultrapure argon. The rivets so produced were observed to have a greatly improved ductility and modulus elasticity as well as approximately a thirty to forty percent improvement in the machineability thereof over rivets such as wrought from titanium base alloy rod or wire. Comparative tests have indicated that the only titanium base alloy rivets available which are capable of being cold-headed without cracking or fracturing are those produced by the process of the present invention. This is dramatically pointed up by the fact that during the tests standard wrought titanium base alloy rivets being cold-headed fractured and shattered to the extent that shrapnel was projected through the test area.

EXAMPLE III A low interstitial contaminant containing titanium base alloy powder produced as set forth, in Example I was isostatically reconsolidated in a suitable press at a pressure approximately 60,000 p.s.i. into the configuration of thin wall tubing having a density of approximately 85% of theoretical. The green compact was sintered and then heat treated as set forth in Example II and was observed to have a sintered density of approximately 96% of theoretical density. The thin wall microscopically porous tube produced in this manner is highly suitable for use in hydraulic systems encountering high operational and surge pressures. Tubes normally utilized in such systems are rated for an operation at a given pressure i.e. 4,000 p.s.i. and a bursting pressure, i.e. 16,000 p.s.i. In this regard, the microscopically porous ductile relatively high modulus elasticity thin wall tubes produced in accordance with the principles of the persent invention would be functional at a specified pressure, i.e. 4,000 p.s.i. but not rupture at a surge pressure of i.e. 16,000 p.s.i. inasmuch as by virtue of the fact that the tube has a uniform microporous nature and consequently when the tube is subjected to normal working pressure 4,000 p.s.i. it is quite functional, but should the working pressure be exceeded and surge to, for example, 16,000 p.s.i. the tube due to this porosity permits the excess pressure to bleed off through the pores rather than cause bursting of the tube. It will therefore be appreciated that such an article may be advantageously utilized in fluid handling systems subjected to relatively high internal surge pressures.

From the foregoing it will be readily apparent that the process of the present invention provides titanium base alloy articles possessing properties not heretofore attainable. The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact process and products shown and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention as claimed.

What is claimed as new is as follows:

1. The powder metallurgy process of making a relatively ductile microscopically porous titanium alloy article characterized by a relatively high modulus of elasticity which comprises the steps of:

producing a finely powdered low interstitial contaminant containing powdered metal from a relatively nonductile, low modulus of elasticity titanium base alloy by comminuting said alloy in a susbtantially inert atmosphere;

isostatically reconsolidating the low interstitial contaminant containing powdered titanium base alloy at prressures in the order of about 40,000 p.s.i. to 100,000 p.s.i. to form a green unsintered machinable article; sintering the green compact in a substantially inert atmosphere at a partial pressure at a temperature in the order of about 2100 F. to 2200 F. for a period of time necessary to produce the desired degree of coalescence; annealing the sintered article at a temperature of about 1750 F. to enhance the desired crystallization of the sintered article and then gradually reducing the temperature of the article to about 1100 F.; and

quenching the annealed article from about 1100 F. to

about room temperature in a cold flow of a substantially inert gas so as to produce a relatively ductile microscopically porous reconsolidated titanium base allow article characterized by a relatively good modulus of elasticity.

2. The process of claim 1 including the step of machining the green unsintered article to substantially final tolerances prior to sintering.

3. The process of claim 1 wherein the titanium base alloy consists of about 6% aluminum, about 4% vanadium and the balance of titanium.

4. The process of claim 1 wherein the titanium base alloy has a minimum titanium content of about 75%.

5. The powder metallurgy process of making a relatively ductile microscopically porous titanium base alloy rivet characterized by the ability to be cold-headed without any significant degree of cracking or fracturing which comprises the steps of:

producing a finely powdered low interstitial contaminant containing powdered metal from a relatively non-ductile, low modulus of elasticity titanium base alloy by comminuting said alloy in a substantially inert atmosphere;

reconsolidating the low interstitial contaminant containing powdered titanium base alloy at pressures in the order to about 40,000 p.s.i. to 100,000 p.s.i. to form a green unsintered rivet; sintering the green compact in a substantially inert atmosphere at a temperature of about 2100 F. to about 2200 F. for approximately four hours;

annealing the sintered rivet at a temperature of about 1725" F. for about 1 hour; and

quenching the annealed rivet from a temperature of 1725 F. down to a temperature of about 1100 F. in about three minutes and then gradually down to about room temperature in a flow of a substantially inert gas so as to produce a relatively ductile reconsolidated titanium base alloy rivet characterized by a relatively good modulus of elasticity which may be cold headed without cracking or fracturing.

6. The powder metallurgy process of making a microscopically porous relatively ductile titanium base alloy thin wall tube which comprises the steps of:

producing a finely powdered low interstitial contaminant containing powdered metal from a relatively non-ductile, low modulus of elasticity titanium base alloy by comminuting said alloy in a substantially inert atmosphere;

reconsolidating the low interstitial contaminant containing powdered titanium base alloy at pressures in the order of about 40,000 p.s.i. to 100,000 p.s.i. to form a green unsintered thin wall tube having a density of approximately of the maximum theoretical density;

sintering the green compact in a non-reactive atmosphere at a temperature of about 2100 F. to about 2200 F. for a sufiicient period of time so as to increase the density of the sintered tube to approximately 96% of the maximum theoretical density; annealing the sintered thin wall tube by cooling the tube to a temperature of about 1725 F. to about 1750 F. and holding at such temperature for a predetermined period of time followed by gradually cooling the tube to about 1000 F. to about 1100" F.; and quenching the tube to about room temperature in a cold inert gas atmosphere to produce a microscopically porous thin wall tube adapted to permit the bleed-off of excessive pressure through the microscopic pores in the walls thereof. v7. The process of claim 6 wherein the titanium base alloy consists of about 6% aluminum, about 4% vanadium and the balance of titanium.

8. The process of claim 6 wherein the titanium base alloy has a minimum titanium content of about 75%.

8 References Cited UNITED STATES PATENTS 2/1968 Ellis 14831 CARL D. QUARFORTH, Primary Examiner A. J. STEINER, Assistant Examiner US. Cl. X.R. 

